Beginner's software bug can crash Boeing 787 Dreamliner worth $200 million
The bug, a classic integer overflow known to everyone who read Programming 101, is in one of the electrical systems responsible for generating power. The vulnerability, which Boeing reported to the FAA, is triggered when a generator has been running continuously for a little more than eight months.
FAA officials have adopted a new airworthiness directive (AD) that airlines will be required to follow, at least until the underlying flaw is fixed.
"This AD was prompted by the determination that a Model 787 airplane that has been powered continuously for 248 days can lose all alternating current (AC) electrical power due to the generator control units (GCUs) simultaneously going into failsafe mode," the FAA memo stated.
"This condition is caused by a software counter internal to the GCUs that will overflow after 248 days of continuous power. We are issuing this AD to prevent loss of all AC electrical power, which could result in loss of control of the airplane."
The memo says Dreamliners have four main generator control units associated with the engine mounted generators. If all of them were powered up at the same time, "after 248 days of continuous power, all four GCUs will go into failsafe mode at the same time, resulting in a loss of all AC electrical power regardless of flight phase."
Boeing is in the process of developing a GCU software upgrade that will remedy the unsafe condition.
The memo doesn't provide additional details about the underlying software bug, however it's easy to see that the problem is in a signed 32-bit integer. ■